Connected: An Internet Encyclopedia
RFC 1661 - 4.1. State Transition Table

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### 4.1. State Transition Table

The complete state transition table follows. States are indicated horizontally, and events are read vertically. State transitions and actions are represented in the form action/new-state. Multiple actions are separated by commas, and may continue on succeeding lines as space requires; multiple actions may be implemented in any convenient order. The state may be followed by a letter, which indicates an explanatory footnote. The dash ('-') indicates an illegal transition.

          | State
          |    0         1         2         3         4         5
    Events| Initial   Starting  Closed    Stopped   Closing   Stopping
    ------+-----------------------------------------------------------
     Up   |    2     irc,scr/6     -         -         -         -
     Down |    -         -         0       tls/1       0         1
     Open |  tls/1       1     irc,scr/6     3r        5r        5r
     Close|    0       tlf/0       2         2         4         4
          |
      TO+ |    -         -         -         -       str/4     str/5
      TO- |    -         -         -         -       tlf/2     tlf/3
          |
     RCR+ |    -         -       sta/2 irc,scr,sca/8   4         5
     RCR- |    -         -       sta/2 irc,scr,scn/6   4         5
     RCA  |    -         -       sta/2     sta/3       4         5
     RCN  |    -         -       sta/2     sta/3       4         5
          |
     RTR  |    -         -       sta/2     sta/3     sta/4     sta/5
     RTA  |    -         -         2         3       tlf/2     tlf/3
          |
     RUC  |    -         -       scj/2     scj/3     scj/4     scj/5
     RXJ+ |    -         -         2         3         4         5
     RXJ- |    -         -       tlf/2     tlf/3     tlf/2     tlf/3
          |
     RXR  |    -         -         2         3         4         5

          | State
          |    6         7         8           9
    Events| Req-Sent  Ack-Rcvd  Ack-Sent    Opened
    ------+-----------------------------------------
     Up   |    -         -         -           -
     Down |    1         1         1         tld/1
     Open |    6         7         8           9r
     Close|irc,str/4 irc,str/4 irc,str/4 tld,irc,str/4
          |
      TO+ |  scr/6     scr/6     scr/8         -
      TO- |  tlf/3p    tlf/3p    tlf/3p        -
          |
     RCR+ |  sca/8   sca,tlu/9   sca/8   tld,scr,sca/8
     RCR- |  scn/6     scn/7     scn/6   tld,scr,scn/6
     RCA  |  irc/7     scr/6x  irc,tlu/9   tld,scr/6x
     RCN  |irc,scr/6   scr/6x  irc,scr/8   tld,scr/6x
          |
     RTR  |  sta/6     sta/6     sta/6   tld,zrc,sta/5
     RTA  |    6         6         8       tld,scr/6
          |
     RUC  |  scj/6     scj/7     scj/8       scj/9
     RXJ+ |    6         6         8           9
     RXJ- |  tlf/3     tlf/3     tlf/3   tld,irc,str/5
          |
     RXR  |    6         7         8         ser/9

The states in which the Restart timer is running are identifiable by the presence of TO events. Only the Send-Configure-Request, Send- Terminate-Request and Zero-Restart-Count actions start or re-start the Restart timer. The Restart timer is stopped when transitioning from any state where the timer is running to a state where the timer is not running.

The events and actions are defined according to a message passing architecture, rather than a signalling architecture. If an action is desired to control specific signals (such as DTR), additional actions are likely to be required.

[p] Passive option; see Stopped state discussion.

[r] Restart option; see Open event discussion.

[x] Crossed connection; see RCA event discussion.

Next: 4.2. States

Connected: An Internet Encyclopedia
RFC 1661 - 4.1. State Transition Table